Formed microchannel heat exchanger

ABSTRACT

A heat exchanger includes a plurality of heat exchange layers stacked in a stackwise direction. Each of the layers includes a first plate and a second plate, each of the first plate and the second plate includes a portion of a first enclosed header, a second enclosed header and at least one flow channel that extends between the first enclosed header and the second enclosed header. The first plate and the second plate are fixedly attached to one another to completely define the first enclosed header, the second enclosed header, and the at least one flow channel. An inlet header is in fluid communication with the first enclosed header of each of the plurality of heat exchange layers to direct a flow of fluid to the heat exchange layers. An outlet header is in fluid communication with the second enclosed header of each of the plurality of heat exchange layers to direct the flow of fluid from the heat exchange layers. The heat exchanger also includes a plurality of fins with each positioned between adjacent heat exchange layers.

BACKGROUND

The present invention relates to heat exchangers, and more particularlyto microchannel heat exchangers that are assembled using formed plates.

Microchannel heat exchangers include a plurality of small channelsthrough which a first fluid flows. The large surface area to volumeratio improves heat transfer efficiency, thereby allowing for the use ofsmaller heat exchangers.

However, microchannel heat exchangers often include channels formed fromextruded tubes that are brazed into the heat exchanger assembly. Thenumber of tubes needed and the likelihood of a failed brazed jointincreases the cost of microchannel heat exchangers.

SUMMARY

In one embodiment, the invention provides a heat exchanger that includesa plurality of heat exchange layers stacked in a stackwise direction.Each of the layers includes a first plate and a second plate, each ofthe first plate and the second plate includes a portion of a firstenclosed header, a second enclosed header and at least one flow channelthat extends between the first enclosed header and the second enclosedheader. The first plate and the second plate are fixedly attached to oneanother to completely define the first enclosed header, the secondenclosed header, and the flow channel. An inlet header is in fluidcommunication with the first enclosed header of each of the plurality ofheat exchange layers to direct a flow of fluid to the heat exchangelayers. An outlet header is in fluid communication with the secondenclosed header of each of the plurality of heat exchange layers todirect the flow of fluid from the heat exchange layers. The heatexchanger also includes a plurality of fins with each positioned betweenadjacent heat exchange layers.

In another construction, the invention provides a heat exchanger thatincludes a plurality of heat exchange layers stacked in a stackwisedirection. Each of the layers includes a first plate and a second plate,each of the first plate and the second plate includes a portion of afirst enclosed header, a second enclosed header and at least one flowpath that extends between the first enclosed header and the secondenclosed header. The first plate and the second plate are fixedlyattached to one another to completely define the first enclosed header,the second enclosed header, and the flow path. A flow device has a firstend connected to the second enclosed header of a first of the pluralityof heat exchange layers and a second end connected to the first enclosedheader of a second of the plurality of heat exchange layers to connectthe first of the plurality of heat exchange layers and the second of theplurality of heat exchange layers in series. An inlet header is in fluidcommunication with the first enclosed header of the first of theplurality of heat exchange layers to direct a flow of fluid to the firstof the plurality of heat exchange layers. An outlet header is in fluidcommunication with the second enclosed header of the second of theplurality of heat exchange layers to direct the flow of fluid from thesecond of the plurality of heat exchange layers. A layer of fins ispositioned between the first of the plurality of heat exchange layersand the second of the plurality of heat exchange layers.

In yet another construction, the invention provides a heat exchangerthat includes a plurality of heat exchange layers arranged in astackwise direction. Each of the heat exchange layers includes an inletand an outlet. A plurality of fins are arranged such that at least onefin is positioned between adjacent heat exchange layers. An inlet headerouter wall defines a central axis and an inner wall is disposed withinthe outer wall to define a first space therebetween. The outer wall iscoupled to at least one of the plurality of heat exchange layers toprovide fluid communication between the first space and the inlet. Afiller plug is disposed within the inner wall to define a second spacetherebetween. The second space is in fluid communication with an inletto receive a flow of fluid. The second space has a flow cross sectionalarea measured normal to the central axis, the flow cross sectional areavarying along the length of the central axis.

Other aspects of the invention will become apparent by consideration ofthe detailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a compressor system including a heatexchanger,

FIG. 2 is a perspective view of a portion of a formed microchannel heatexchanger suitable for use with the compressor of FIG. 1;

FIG. 3 is a section view of the heat exchanger of FIG. 2, taken alongline 3-3 of FIG. 2;

FIG. 4 is a section view of a header of the heat exchanger of FIG. 3taken along line 4-4 of FIG. 3;

FIG. 5 is a section view of a header of the heat exchanger of FIG. 3taken along line 5-5 of FIG. 3;

FIG. 6 is a section view of a header of the heat exchanger of FIG. 3taken along line 6-6 of FIG. 3;

FIG. 7 is an exploded perspective view of a portion of the heatexchanger of FIG. 2 illustrating a formed microchannel plate;

FIG. 8 is a top view of another formed microchannel plate suitable foruse with the heat exchanger of FIG. 2;

FIG. 9 is a perspective view of another heat exchanger including severalformed microchannel plates similar to those of FIG. 7 connected inseries; and

FIG. 10 is a perspective view of another heat exchanger includingseveral formed microchannel plates similar to those of FIG. 8 connectedin series.

DETAILED DESCRIPTION

Before any embodiments of the invention are explained in detail, it isto be understood that the invention is not limited in its application tothe details of construction and the arrangement of components set forthin the following description or illustrated in the following drawings.The invention is capable of other embodiments and of being practiced orof being carried out in various ways.

FIG. 1 schematically illustrates a gas compression system 10 thatincludes a compressor 15, a prime mover 20, and a dryer 25. Thecompression system 10 includes a refrigeration system 30 and mayoptionally include a second fluid system. The refrigeration system 30includes a refrigerant compressor 40, a condenser 45, and an expansiondevice 50 as is typical with refrigeration systems 30. The second fluidsystem, if included includes a pump and a reservoir for a second fluidthat can be used as a heat sink to reduce the peak load on therefrigeration system 30.

The prime mover 20 can include an electric motor, an engine (e.g.,internal combustion, rotary, turbine, diesel, etc.), or any other drivecapable of providing shaft power to the compressor 15.

The compressor 15 includes an inlet 55 that provides a fluid flow pathfor incoming gas to be compressed and an outlet 60 through whichcompressed gas is discharged. The illustrated system is an open systemfor compressing air. Thus, air is drawn into the compressor 15 from theatmosphere and is compressed and discharged through the outlet 60.However, it should be understood that the compressor system 10illustrated in FIG. 1 could be employed to compress many other gasses,and could be employed in a closed cycle (e.g., refrigeration system) ifdesired.

The compressor 15 includes a shaft 62 that is driven by the prime mover20 to rotate a rotating element of the compressor 15. In someconstructions, the compressor 15 includes a rotary screw compressor thatmay be oil flooded or oil less. In the oil flooded constructions, an oilseparator would be employed to separate the oil from the compressed airbefore the air is directed to the dryer 25. In other constructions, acentrifugal or other compressor arrangement may be employed. Of course,single stage or multi-stage compressors could also be employed as may berequired for the particular application.

The dryer 25 includes an air inlet 65 that receives compressed air fromthe compressor 15. In an open air compression system 10 as illustratedin FIG. 1, the compressed air includes moisture or water that is presentin the air that is drawn into the compressor 15. During compression, themoisture is carried by the flow of compressed air as entrained liquid ora quantity of moisture. The dryer 25 includes a heat exchanger 80 andoperates to separate a portion of the entrained liquid or quantity ofmoisture from the flow of compressed air, discharges the liquid from adrain 70 on the bottom of the dryer 25, and discharges the flow ofsubstantially dry compressed air from an air outlet 75 at the top of thedryer 25.

The dryer 25 of FIG. 1 delivers a chilled refrigerant to the heatexchanger 80 which acts as the evaporator of the refrigeration system 30to cool the air and moisture within the air to condense and remove aportion of the moisture. In one construction, the refrigerant flowsthrough the heat exchanger 80 and the air flows over the heat exchanger80 as will be described.

With reference to FIG. 2, one possible arrangement of the heat exchanger80 is illustrated. The heat exchanger 80 includes an inlet header 85, anoutlet header 90, a plurality of enclosed layers 95, and a plurality ofcorrugated members 100. Each corrugated member 100 includes a corrugatedsheet of material that partially defines a plurality of flow channels105. Each corrugated member 100 attaches to at least one adjacentenclosed layer 95 to more fully enclose the flow channels 105. Inpreferred constructions, the corrugated sheet of material is formed froma material well-suited to heat transfer applications such as metal andparticularly aluminum, copper, stainless steel, and the like.

Each enclosed layer 95 includes an upper plate 110 and a lower plate 115that are attached to one another. In preferred constructions, the upperplate 110 and the lower plate 115 are identical. Each plate 110, 115 isstamped or otherwise formed to partially define a formed inlet header120, a formed outlet header 125, and a plurality of internal channels130. The upper plate 110 and the lower plate 115 are then positioned ina facing relationship such that the formed portions 120, 125, 130 extendaway from the opposite plate such that when the plates 110, 115 areattached to one another they cooperate to completely define and enclosethe formed inlet header 120, the formed outlet header 125, and theplurality of internal channels 130. Each of the internal channels 130extends substantially linearly from the formed inlet header 120 to theformed outlet header 125 and are substantially parallel to one another.In other constructions, the channels 130 may be curved and/or notparallel to one another. In addition, the channels 130 can be formedwith smooth inner walls or could include bumps or otherturbulence-inducing elements that enhance the heat transfer between theplates 110, 115 and the medium (refrigerant in the illustratedconstruction) flowing through the channels 130.

Each of the formed inlet header 120 and the formed outlet header 125includes a tube portion 135 that extends from the respective header 120,125 to the edge of the plates 110, 115. A first tube 140 is sized to fitwithin the tube portion 135 of the formed inlet header 110 and providesfor fluid communication between the inlet header 85 and the formed inletheader 110. A second tube 145 is sized to fit within the tube portion135 of the formed outlet header 125 and provides for fluid communicationbetween the outlet header 90 and the formed outlet header 125.

As illustrated in FIG. 3, the inlet header 85 includes an outer wall150, a first cap 155, a second cap 160, a ribbed wall 165, and a fillerplug 170. The outer wall 150 includes a substantially cylindrical tubethat is open at the top and bottom and that defines a longitudinal orcentral axis 175. The outer wall 150 includes an inlet aperture 180 anda plurality of outlet apertures 185 that each receives one of the firsttubes 140. The first cup 155 scalingly attaches to the outer wall 150near one end and the second cap 160 scalingly attaches to the outer wall150 near the second opposite end to fully enclose an interior 190 of theouter wall 150.

The ribbed wall 165 is disposed within the interior 190 of the outerwall 150 and extends from the first cup 155 to the second cup 160.Annular ribs 195 extend around the circumference of the ribbed wall 165and sealingly contact the outer wall 150. The annular ribs 195, theribbed wall 165, and the outer wall 150 cooperate to define a number ofannular spaces 200. In preferred constructions, the number of annularspaces 200 is equal to the number of enclosed layers 95 such that one ofthe first tubes 140 extends through one of the outlet apertures 185 ofthe outer wall 150 to provide fluid communication between the annularspace 200 and the first tube 140. Of course, other constructions may bearranged with more or fewer annular spaces 200 than enclosed layers 95.

The ribbed wall 165 includes an inlet aperture 205 near one end and aplurality of outlet apertures 210 with each outlet aperture 210 disposedadjacent one of the annular spaces 200. An inlet tube 215 extends from asource of fluid (downstream of the expansion device 50), through theinlet aperture 180 of the outer wall 150 and through the inlet aperture205 of the ribbed wall 165 to provide for a flow of fluid into a space220 within the ribbed wall 165.

The filler plug 170 is disposed in the space 220 within the ribbed wall165 and extends from the first cap 155 to the second cap 160. The fillerplug 170 cooperates with the ribbed wall 115 to define an annular flowarea 225 that extends between the first cap 155 and the second cap 160.The filler plug 170 is substantially cylindrical and includes a taperedportion 230 arranged such that the flow area as measured normal to thecentral axis 175 of the filler plug 170 is non-uniform. The areadecreases as the distance from the inlet 205 increases. FIGS. 4-6illustrate this decrease in area as the distance from the inlet 205increases.

Before proceeding, it should be noted that the inlet header 85 and theoutlet header 90 can be substantially the same. As such, the outletheader 90 will not be described in detail other than to note that anyfeatures described with regard to the inlet header 85 as an “inlet”would be an “outlet” with regard to the outlet header 90 and visa versa.In preferred constructions, the inlet header 85 and outlet header 90 arenot identical. Typically, the inlet header 85, particularly when theheat exchanger is an evaporator, uses the illustrated construction tocarefully control the equal distribution of the evaporating liquid gasmixture to the various enclosed layers 95. Generally, the outlet header90 can be a simple tube. For condensers, both the inlet header 85 andthe outlet header 90 can be plain tubes if desired.

To assemble the heat exchanger 80 of FIGS. 1-7, the headers 85, 90 firstformed. The headers 85, 90 can be stacked or arranged as illustrated inFIG. 3 and then brazed in a single brazing operation. Alternatively, thecomponents can be attached to one another and brazed, soldered, welded,or the like in a step-by-step fashion.

In one arrangement, the filler plug 170 and the ribbed wall 165 aresealingly attached to each of the first cap 155 and the second cap 160to enclose the space 220. The filler plug 170, ribbed wall 165, firstcap 155, and second cap 160 are then inserted into the outer wall 150and sealingly attached to the outer wall 150 to enclose the annularspaces 200. Finally, the inlet tube 215 (outlet tube for the outletheader 90) and the first tubes 140 (second tubes 145 for the outletheader 90) are inserted through the outer wall 150, with the inlet tube215 also passing through the ribbed wall 165. The tubes 140 are thensealingly attached to the components through which they pass to completethe assembly.

In a preferred arrangement, the components of the headers 85, 90 areclad with a low melting point material and are positioned as illustratedin FIG. 3. The entire assembly is then heated to a desired temperatureto melt the low melting point material and scalingly attach all of thecomponents to the components that they contact.

FIG. 7 illustrates a partially exploded view of the heat exchanger 80 toillustrate the assembly process. In some constructions, each of thecomponents is clad with a low melting point material to allow brazing ofthe entire assembly in one brazing operation. The upper plate 110 andlower plate 115 of each enclosed layer 95 are thus positioned adjacentone another in the desired facing relationship. The first tube 140 andsecond tube 145 are inserted between the upper plate 110 and lower plate115 and are inserted into the respective inlet/outlet apertures 180 ofthe inlet header 85 and the outlet header 90. Corrugated members 100 arepositioned between the enclosed layers 95 and, if desired on the topand/or bottom of the uppermost and lowermost enclosed layer 95. Theentire assembly is then heated to a desired temperature to melt the lowmelting point material and sealably attach all of the components to makea single unitary structure. In other constructions, the components areassembled in multiple steps. For example, in one construction, the upperplate 110 and lower plate 115 of the various enclosed layers 95 arefirst attached to one another. Next, the first tube 140 and the secondtube 145 are attached to each of the enclose layers 95 and corrugatedmembers 100 are attached to the enclosed layers 95 as required. Finally,the first tube 140 and the second tube 145 of each enclosed layer 95 areattached to the respective inlet header 85 and outlet header 90 tocomplete the assembly.

In operation, a flow of fluid passes from a source such as from thedischarge of the expansion device 50 of the refrigeration system 30 intothe inlet header 85 via the inlet tube 215. With reference to FIG. 3,the flow is directed to the inner space 220 defined by the cooperationof the filler plug 170 and the ribbed wall 165. As the flow passes fromthe first end of the inner space 220 toward the second end, portions aredischarged from the inner space 220 to the annular spaces 200 via theoutlet apertures 185. The flow velocity within the header 85 is afunction of the mass flow and the area, as the density of the fluidremains substantially constant. As flow is discharged, the flow velocitywould decrease if the flow area of the inner space 220 were uniform.However, as illustrated in FIGS. 3-6, the flow area of the inner space220 actually decreases as the mass flow decreases, thereby producing asubstantially uniform flow rate within the inlet header 85. The uniformflow rate within the header 85 improves the distribution of fluid to thevarious enclosed layers 95 to assure relatively uniform flow to eachenclosed layer 95.

The flow discharged from the outlet apertures 185 collects in theannular spaces 200 between the ribs 195 and is directed into the desiredenclosed layers 95. With reference to FIG. 2, the flow passes throughthe tube portion 135 of the formed inlet header 120 and is thendistributed to the various internal channels 130. The flow then flows ina generally first direction 235 to the formed outlet header 125 and thetube portion 135 of the formed outlet header 125. As noted above, insome constructions, the internal channels may zig zag or move in anothernon-linear direction if desired. However, ultimately, the fluid movesfrom one end of the enclosed layer 95 to an opposite end and as suchmoves in the generally first direction 235.

With reference to FIG. 3, the flow then enters the annular spaces 200 ofthe outlet header 90 and is collected in the various annular spaces 200between the ribs 195 of the ribbed wall 165. The flow passes from theannular spaces 200 to the inner space 220 via the inlet apertures 185formed in the ribbed wall 165. As the flow enters the inner space 220and flows toward the outlet tube 215, the quantity of fluid increases.To maintain the flow velocity, the flow area of the inner space 220increases in the flow direction. As discussed, the increased space is aresult of the increase in the size of the tapered portion 230 of thefiller plug 170. The flow then exits the outlet header 90 via the outlettube 215 and, as illustrated in FIG. 1 returns to the refrigerantcompressor 40 to complete the refrigeration cycle. Thus, the heatexchanger 80 of FIG. 1 operates as an evaporator to cool the air flow tocondense water from the air flow to produce the desired flow of dry air.

A second fluid that is being heated or cooled by the fluid in theenclosed spaces 95 is directed through the channels 105 defined by thecorrugated members 100. The flow generally flows in a second direction240 that is normal to the first direction 235. However, zig zags orother non-linear flow paths could be defined by the corrugated members100. In addition, the corrugated members 100 could be arranged toproduce a diagonal flow or even a flow that is substantially parallel tothe flow in the enclosed layers 95 if desired.

FIG. 8 illustrates another arrangement of an enclosed layer 245 suitablefor use with the heat exchanger 80 of FIGS. 1-7. The enclosed layer 245of FIG. 8 is formed and assembled in much the same manner as wasdescribed with regard to FIGS. 1-7. The construction of FIG. 8 includesan enclosed inlet header 250 and an enclosed outlet header 255 as withthe construction of FIGS. 1-7. However, rather than being disposed onopposite ends of the enclosed layer 245, the enclosed inlet header 250and the enclosed outlet header 255 are disposed on the same side of theenclosed layer 245. Thus, the enclosed channels 260 that extend from theenclosed inlet header 250 to the enclosed outlet header 255 areU-shaped. The flow within the enclosed channels 260 flows in a firstdirection 235, much as with the construction of FIGS. 1-7, turns at oneend of the enclosed layer 245 and then returns in a direction oppositethe first direction 235. A thermal break 263 is positioned between thechannels 260 that are directing fluid in opposite directions to inhibitheat transfer between the channels 260. In constructions employing theenclosed layer 245 of FIG. 8, the inlet header 250 and the outlet header255 would be positioned adjacent the same end of the enclosed layer 245rather than on opposite ends as illustrated in FIG. 2.

FIG. 9 illustrates another arrangement of the enclosed layers 95 ofFIGS. 1-7. The enclosed layers 95 and the remainder of the complete heatexchanger 80 are substantially the same as the enclosed layers 95 andthe remainder of the heat exchanger 80 illustrated in FIGS. 1-7.However, rather than connecting one end of each enclosed layer 95 to theinlet header 85 and the other end to the outlet header 90, the enclosedlayers 95 are arranged to direct the flow through three enclosed layers95 before discharging the fluid. The flow passes in a first direction235 through a first enclosed layer 95 a, through a flow device 265(e.g., tube, pipe, conduit, etc.) to a second enclosed layer 95 b andflows in a second direction substantially opposite the first direction235. The flow then passes through a second flow device 270 to a thirdenclosed layer 95 c that directs the fluid in the first direction 235.After passing through the third enclosed layer 95 c, the fluid isdischarged from the heat exchanger 80.

In yet another arrangement similar to the one of FIG. 9, the flow passesthrough only the first two enclosed layers 95 and is discharged. In thisarrangement, the inlet header 85 and the outlet header 90 are bothpositioned on the same side of the enclosed layers 95, rather than onopposite sides as in the arrangement of FIG. 9.

In still another arrangement illustrated in FIG. 10, the enclosed layers245 of FIG. 8 are arranged such that the flow passes through a firstenclosed layer 245 a and a second enclosed layer 245 b before the flowis discharged. Thus, the construction of FIGS. 1-7 produces a heatexchanger 80 in which the flow in the enclosed layers 95 flows acrossthe corrugated members 100 once and is discharged. The construction ofFIG. 8 provides an arrangement in which the flow crosses the corrugatedmembers 100 twice before it is discharged. The construction of FIG. 9provides three crossings of the corrugated members 100 while theconstruction of FIG. 10 provides four. As one of ordinary skill willrealize, there are other arrangements of the various constructionsillustrated herein that can achieve different degrees of heat exchange.For example, the enclosed layer 245 of FIG. 8 could be combined with theenclosed layers 95 of FIGS. 1-7 to achieve three crossings using onlytwo enclosed layers 95, 245. Thus, the invention should not be limitedto the constructions illustrated and discussed herein.

Thus, the invention provides, among other things, a heat exchanger 80that includes a plurality of formed channels 130 that is easilyconstructed. Various features and advantages of the invention are setforth in the following claims.

1-18. (canceled)
 19. A heat exchanger comprising: a plurality of heatexchange layers arranged in a stackwise direction, each of the heatexchange layers including an inlet and an outlet; an inlet headerfluidly coupled to the plurality of heat exchange layers, the inletheader having an outer wall with a central axis extending along alongitudinal length thereof and an inner wall disposed within the outerwall to define a first space therebetween, the outer wall coupled to atleast one of the plurality of heat exchange layers to provide fluidcommunication between the first space and the inlet; and a filler plugdisposed within the inner wall to define a second space therebetween,the second space in fluid communication with an inlet conduit to receivea flow of fluid, the second space having a flow cross sectional areanormal to the central axis, the flow cross sectional area varying alongthe length of the central axis.
 20. The heat exchanger of claim 19,wherein the inner wall includes a plurality of ribs that cooperate withthe outer wall of the inlet header to divide the first space into aplurality of separate annular spaces.
 21. The heat exchanger of claim20, wherein the number of annular spaces is equal to the number of heatexchange layers.
 22. The heat exchanger of claim 19, wherein the fillerplug includes a portion having a non-circular cross-section taken normalto the longitudinal axis, the filler plug cross-section varying alongthe length of the central axis.
 23. The heat exchanger of claim 19,wherein the inner wall includes an inlet aperture near a first end, theinlet aperture arranged to receive the flow of fluid, and wherein theflow cross sectional area of the second space decreases as the distancefrom the inlet increases.
 24. The heat exchanger of claim 20 wherein aportion of each rib engages with the outer wall of the inlet header. 25.The heat exchanger of claim 20 further comprising an outlet apertureformed through the inner wall proximate each of the annular spaces. 26.The heat exchanger of claim 19, wherein each of the heat exchange layersinclude a first plate and a second plate, each of the first and thesecond plates includes a portion of a first enclosed header, a secondenclosed header and at least one flow channel that extends between thefirst enclosed header and the second enclosed header, the first plateand the second plate attached to one another to define the firstenclosed header, the second enclosed header, and the flow channel. 27.The heat exchanger of claim 26 further comprising an outlet header influid communication with the second enclosed header of at least one ofthe plurality of heat exchange layers.
 28. The heat exchanger of claim27, wherein the outlet header includes an inner wall and an outer wallspaced apart from one another to form an outer annual flow area.
 29. Theheat exchanger of claim 28 further comprising a filler plug positionedinward of the inner wall of the outlet header.
 30. The heat exchanger ofclaim 29, wherein the filler plug includes a non-circular cross-sectionthat varies along a length thereof.
 31. The heat exchanger of claim 29further comprising an inner annual flow area defined by a space betweenthe filler plug and the inner wall of the outlet header.
 32. The heatexchanger of claim 31 wherein the inner annual flow area decreases fromone end to an opposing end of the outlet header.
 33. The heat exchangerof claim 28, wherein the inner wall of the outlet header includes aplurality of ribs positioned along a longitudinal length thereof. 34.The heat exchanger of claim 33, wherein each of the ribs protrudeoutward to engage with the outer wall of the outlet header to divide theouter annual flow area into a plurality of separate annular spaces. 35.The heat exchanger of claim 34 further comprising an outlet apertureformed through the inner wall proximate each of the annular spaces. 36.The heat exchanger of claim 27 further comprising at least one finpositioned between adjacent heat exchange layers; and wherein the atleast one flow channel directs the fluid between the inlet header andthe outlet header and the at least one fin direct a second fluid in adirection that is substantially normal to a flow direction of the fluid.37. The heat exchanger of claim 26, wherein the at least one flowchannel extends in a substantially U-shape configuration from the firstenclosed header to the second enclosed header disposed adjacent to oneanother at a same end of the heat exchange layer.
 38. The heat exchangerof claim 37, wherein the at least one U-shaped flow channel defines afirst flow leg that directs flow in a first direction and a second flowleg that directs the flow in a second direction opposite the firstdirection.
 39. The heat exchanger of claim 38 further comprising athermal break positioned between the first flow leg and the second flowleg in a heat exchange layer.
 40. The heat exchanger of claim 26,wherein the first plate is substantially the same as the second plate.